In conventional semiconductor devices, a chip in package is attached to a substrate by a die-attach material. There are two major types of forming die-attach materials where one is in either paste or liquid disposed by printing or dispensing. Another one is utilizing a die-attach tape where the die-attach tape is preformed as a tape in solid state and then attached to a substrate. The former has the advantages of saving die-attach materials with flexible printing die-attaching area, however, it is very sensitive to substrate warpage leading to bleeding of die-attach materials. Since solder masks are disposed on both top and bottom surfaces of the substrate, therefore, the substrate warpage is not an issue for now. But when the substrate structure is changed, the die-attach material has to be changed as well.
As shown in FIG. 1, a conventional semiconductor package 100 primarily comprises a substrate 110, a chip 120, a die-attach tape 130, a plurality of bonding wires 140, and an encapsulant 150. The substrate 110 comprises a core layer 111 and only one bottom solder mask 112 disposed over the bottom surface 114 of the core layer 111. Since there is no solder mask disposed on the top surface 113 of the core layer 111, therefore, the die-attach tape 130 is disposed directly to the core layer 111 to adhere the chip 120. The bonding pads 121 of the chip 120 are electrically connected to the corresponding bonding fingers 116 of the substrate 110 by the bonding wires 140 passing through the wire-bonding slot 115 of the substrate 110. The encapsulant 150 encapsulates the chip 120 and the bonding wires 140. A plurality of solder balls 160 are bonded to the ball pads 117 of the substrate 110. The material of the core layer 111 of the substrate 110 is made of glass fiber reinforced resin which has better adhesion to the die-attach tape 130 or other resin-based die-attach materials to enhance die-attaching strength to the chip 120. Since only the bottom solder mask 112 is disposed on the bottom surface 114 of the substrate 110, substrate warpage become worse, especially using substrate strips for semiconductor packaging, leading to difficulties of printing liquid-type die-attach materials directly on the core layer 111 of the substrate 110. Moreover, a substrate strip with severe substrate warpage can not easily be transported nor handled by the packaging equipment during packaging processes. Another method to manufacture the conventional semiconductor package 100 is to singulate the substrate 110 into individual substrate units to reduce substrate warpage. However, it is very difficult to print liquid-type die-attach materials on each individual substrate unit, moreover, individual substrate units are also very difficult to transport and handle by the packaging equipment during packaging processes. Handling individual substrate units will greatly increase packaging costs.